Flutter_20230413_00. Flutter 입문

1. What is Class ? (Lec 35)

- Dart is an object-oriented language.

- Object is created by calling the constructor of a class

- This simply means that Class is a blueprint of making/customizing Object.

 

2. Building widgets + Restructuring (Lec 36~37)

class GradientContainer extends StatelessWidget {
  // GradientContainer({key}): super({key: key});
  const GradientContainer({super.key});

  // constructor: initialize
  // key will recieved and forward it to superClass
  // const is this is ta class that can be optimized that can be
  //[reused] !!
  
  @override
  Widget build(BuildContext context) {
    return Container(
      decoration: const BoxDecoration(
          gradient: LinearGradient(
        colors: [Color.fromARGB(255, 4, 2, 80), Color.fromARGB(255, 45, 7, 98)],
        begin: Alignment.topLeft,
        end: Alignment.bottomRight,
      )),
      child: const Center(
        child: Text(
          'Hello World!',
          style: TextStyle(color: Colors.white, fontSize: 28),
        ),
      ),
    );
  }
}

 

3. Variables (Lec 38~ 42)

- final vs const 

  : final and const should not be changed. 

  : final은 실행시, const는 빌드시 값을 가지고 있어야함.

 

double? number = 1; // type ? will allow to keep null
double number = null; // Error

dynamic message = 'Hello, World';

//able to change type
message = 8;

 

- reformat

import 'package:flutter/material.dart';

class GradientContainer extends StatelessWidget {
  // GradientContainer({key}): super({key: key});
  // constructor: initialize
  // key will recieved and forward it to superClass
  // const is this is ta class that can be optimized that can be [reused] !!
  const GradientContainer(this.text, {super.key});
  // => same as below two lines
  // const GradientContainer(String text1, {super.key}): text1 = text2;
  // final String text2;

  // this.text means when it build, dart look for the class variable with that name, and mapped if there is a same name.
  // when this.text is added, const should not be front because , the text might be changed.
  // -> however if final is added, add const because it will always be the same object.

  final String text; // this is used to call from inside => only be set once and static cannbe set to final.

  @override
  Widget build(BuildContext context) {
    return Container(
      decoration: const BoxDecoration(
          gradient: LinearGradient(
        colors: [Color.fromARGB(255, 4, 2, 80), Color.fromARGB(255, 45, 7, 98)],
        begin: Alignment.topLeft,
        end: Alignment.bottomRight,
      )),
      child: Center(
        child: Text(
          text,
          style: const TextStyle(color: Colors.white, fontSize: 28),
        ),
      ),
    );
  }
}